1. Field of the Invention
Embodiments of the present invention relate, in general, to high throughput channel operation in a mesh wireless local area network.
2. Relevant Background
The Institute of Electrical and Electronics Engineers (IEEE) 802.11s is a draft IEEE 802.11 amendment for mesh networking, defining how wireless devices can interconnect to create a WLAN mesh network, which may be used for static topologies and ad-hoc network. 802.11 is generally a set of IEEE standards that govern wireless networking transmission methods. A wireless mesh network is a communications network made up of radio nodes organized in a mesh topology. Wireless mesh networks often consist of mesh clients, mesh routers and gateways. The mesh clients are often laptops, cell phones and other wireless devices while the mesh routers forward traffic to and from the gateways which may, but need not, connect to the Internet. The coverage area of the radio nodes working as a single network is sometimes called a mesh cloud. Access to this mesh cloud is dependent on the radio nodes working in harmony with each other to create a radio network. A mesh network is reliable and offers redundancy. When one node can no longer operate, the rest of the nodes can still communicate with each other, directly or through one or more intermediate nodes.
In the initial Wireless Local Area Network (WLAN) technology, a data rate of 1 to 2 Mbps was supported by the use of frequency hopping, spread spectrum, and infrared communication using a frequency of 2.4 GHz in accordance with the IEEE 802.11 standard. Today IEEE 802.11n provides up to 600 Mbps. The IEEE 802.11 standard has developed or is developing a variety of technical standards for improvement in quality of service (QoS), compatibility of an access point (AP) protocol, security enhancement, wireless resource measurement, wireless access in vehicular environment, fast roaming, wireless mesh network, inter-working with external networks, wireless network management, and the like.
FIG. 1 is a diagram of a mesh network 100 in accordance with the present invention and as known to one skilled in the relevant art. The mesh network 100 comprises a plurality of interconnected mesh points 130, 135. The mesh network 100 may also include a mesh portal 120. The mesh portal 120 is a mesh point that has a connection with an external network 110, (e.g., a wired network). Some of the mesh points may be mesh APs 135. Each of the mesh APs 135 is a mesh point that also works as an AP in its own basic service set 160, 170. A mesh AP 135 can act, in one instance, as a non-mesh AP to serve local stations 150 in its BSS 160, 170, and in another instance, act as a wireless bridge to receive, forward and route packets through the mesh network 100.
Recall that a “wireless mesh network” can support direct communication between plural wireless stations having a relay function. In view of functionality, a distribution system (DS) for plural APs can be replaced with an inter-operable wireless link or a multi-hop path between the plural wireless stations. In the mesh network, one wireless station can set up a peer-to-peer wireless link (peer link) with one or more neighboring wireless stations, thereby constructing a more flexible network. Thus, plural communication paths can exist between two wireless stations. Among them, the direct communication paths between two wireless stations are called a wireless mesh link or a mesh peer link or a peer link. In a mesh network, wireless stations are called mesh points (MP). A wireless station performing the function of an AP is called a mesh access point (MAP).
Such a wireless mesh network has advantages, such as flexibility in constructing a network, reliability due to bypass paths, reduction in power consumption due to a decrease in communication distance. More specifically, it is possible to construct a flexible network by using the mesh network even in places not including any wired communication network. In the mesh network, the plural MPs can be connected to each other to guarantee plural bypass paths. Accordingly, even when one MP is out of order, data can be transmitted through another path. In the mesh network, since the communication can be made through a neighboring MP, it is possible for terminals to communicate with lower power.
IEEE 802.11s provides a means to form a mesh wireless backhaul with IEEE 802.11 WLAN technology. Mesh networks, also known as multi-hop networks, enable data packets to be relayed more than once in order to reach their destination. This presents a different paradigm as compared to the original WLAN standard, which addresses only star topologies for stations (STAs) to be connected to an access point, effectively using single hop communications through a basic service set (BSS).
IEEE 802.11s addresses network nodes that form a mesh network and the WLAN mesh operation in the backhaul that is transparent to all STAs. This means that, similar to legacy IEEE 802.11 WLAN, STAs still connect to an AP, (i.e., mesh AP having a mesh capability), through a BSS. The mesh AP interfaces to other mesh points, which forward and route traffic through the mesh network to a destination. The destination may be a mesh portal, which routes the traffic to the external network, or may be another mesh AP attached to the mesh network. By choosing this approach, even legacy STAs may still operate in a mesh-enabled WLAN. The communication between STAs and a mesh AP in a BSS is completely independent from the mesh network.
The IEEE 802.11n is another specification for providing a high throughput (HT) WLAN. Some of the IEEE 802.11n throughput-enhancing features are aggregation, enhanced block acknowledgement (BA), reverse direction grant, power save multiple poll (PSMP), and operational bandwidth. In IEEE 802.11n, a data rate is increased by annexing or bonding two adjacent channels. The data rate increase is also achieved by using several more data tones, with 802.11 40 MHz operation relative to 2.times.20 MHz channel occupancy with 802.11a/g. However, not all IEEE 802.11n devices may support 40 MHz operation and, therefore, the transition of operation from 20 MHz to 40 MHz must be managed efficiently. In order to achieve this, the IEEE 802.11n standard provides some channel management mechanisms.
In IEEE 802.11n, three operating modes are allowed according to bandwidth and BSS capability: 20 MHz operation, 20/40 MHz operation and Phased Coexistence Operation (PCO). Each of these modes has associated rules of operation. In a 20 MHz operation, all STAs will operate only in a 20 MHz mode whether or not the STAs are 20 MHz or 20/40 MHz capable. In a 20/40 MHz operation, STAs choose the bandwidth by using a transmission channel width action message. In addition, a 40 MHz device will protect its transmission with legacy control frames, such as request-to-send (RTS) or clear-to-send (CTS) frames, if the AP of its BSS indicates that there are 20 MHz and/or legacy STAs in the BSS. In the PCO mode, which is an optional mechanism, the BSS alternates between 20 MHz and 40 MHz modes.
There are three operation modes in the current 802.11 standard: infrastructure BSS, independent BSS and mesh network. In infrastructure BSS, an AP is the controller of the BSS. In independent BSS, there is no central controller and no association between STAs. In mesh network, there is no central controller but neighbor MPs associated with each other 802.11n has features that does not require central controller or peer coordination, and features that require central controller or peer coordination.
The features that do not require central controller or peer coordination can be used in a mesh network without any change after the addition of HT capability to beacon and peer link frames. These capabilities include Aggregated-MAC Service Data Unit (A-MSDU), Aggregated-MAC Protocol Data Unit (A-MPDU), enhanced block acknowledgement, reverse direction grant, beam forming and antenna selection (ASEL).
In IEEE 802.11s, HT information elements control the operation of HT STAB in the mesh network. To effect such control, an infrastructure BSS uses all fields in the HT information element to define the operation of the HT STAB independent BSS use fields that are not reserved to define the operation of HT STAB. Unfortunately, it is unclear what fields will be used or reserved in a mesh network, and it is not clear how features such as power save multi-poll, HT protection, Space Time Block Coding (STBC) operation, 20/40 MHz operation, and phased coexistence operations will be used, or whether features such as PSMP or PCO operations should be allowed at all.
A need therefore exists to identify HT features in a IEEE 802.11s mesh network. These and other deficiencies of the prior art are addressed by one or more embodiments of the present invention.